Safety-box for electric circuits



No Model. M W. L. STEVQN SAFETY BGX E02 ELEGTMG UmGUTS. N0. 316,()77. ate Ap?, 2L 'Lu o the fusion of the` safety-strip,

UNITED STATES PATENT Orifice.

WILLIAM STEVENS', or Bosrolc, MASSACHUSETTS.-

1-S',tijm-y.serI Fo R' ELEYCTRI C `Gl CU TS? sncIrI'cAr'ioN forming pan of Letters atene'No. slslofnfdatea prix 21, '1an-a. A

" apprenait mea 'september mien. (no model.)

To all whom. it may concern..-

Be it known that I, .WILLIAM L. STnvENS, acitizen of theUnited States, and a resident of Boston, in the county of Suffolk and State of 5 Massachusetts, have invented certain new and usefulImprovernets in Safety-Boxes for Electric Circuits, of which the following is aspeciiication, reference benghad to the d rawings accompanying and forming a part ofthe saine.

The object of my present invention is to pro duce 'a safety strip or link for `use in circuits carrying currents of high tension which shall fuse when the flow of current becbmesabnormal', and which shall prevent the continuance i5 of such. I'low byvpreventing the formation of the aro which, in devices heretofore devised, is apt to follow the disruption of the metallic pathof the current.

In carrying out my invention I select strips zo of a fusible metal or alloy of proper length and cross-section, and incluse them in a sheath or envelope of non-conducting incombustible material. Such envelopes or sheaths I make of two'strips of asbestos paper or similar substancesecu'red together by glue with the fusible strip between them.- These strips I subject to pressure while drying.

For applying the safetystrips l use a split wooden cylinder with permanent contacts secured thereto, to which the ends ofthe safetyi strips and the wires of the circ t are co'nnected.. I also usea clamping dev ce for holding the two portions of the cylinder together, and for maintaining the connections perfect.- With safetyboxes thus' constructed I have found it possible to short-circuit the current of forty are lamps 'through a strip three or four inches in length without the formation of an are between the terminal contacts. Thisi 4.o highly important result is due, so far as I havegbecn able to ascertain, to the following causes: .By gluing or cementiug tho Strips of asbestus overa fusible strip under pressure a solid bod'y is formed, in which the space leftbythe fusion of the metal strip 'is so con- Y jtractedas toprevent orobeok the passage of l the are.' This effect is still further increased by the use of the clamping' device, which operates to close upcompletely the space left by by compressing the yielding sides of the asbestns sheath tomother. and thus interposing a non-conducting body between theterminals of the safetybox. l

I will Vdescribe the most convenient and 5 practicable form of safety-box constructed on this principle which I have devised by refer- Yence to the accompanying drawings.

. Figure 1 is a perspective View of the box in condition for use. Fig. 2 is a perspective view of the several parts of the same detached. Fig. 3 isl a view of an inclosed safetystrip, showing a portion of one of the infusible Strips removed.

A is astrip or ribbon of fusible metal or.65 alloy, the length or crosssectioncf which will vary according to the current which it is designed to carry without fusing.

B C are dat strips or sheets of asbestos paper or any like ini'usible non-conducting sub-l stance. They are somewhat shorter than strip` A, and are brought together over the strippA and fastened by glue. Pressure is appliedv while the glue is drying.

D E are the two halves of a split wooden cylinder. At the ends of part D are Secured metal plates d, to which the line-wires of a circuit are connected by the screws a., or-otherwise. An inclosed safety-strip is 'laid on the face of the part E, and its projecting .ends So clamped under spring-plates b t; Vsheu the I two parts D E are brought together, the cir- -cuit will be, completed betweenthe plates@ ythrough the strip A.

f Any convenient forni oi clamp may be used to bind the parts together., That shown ccnsiste of two wooden blocks', .F G, secured to get-her by the screws g. This safety-box may be inserted at any desiredpoint in a circuit, and used generally for all purposes to which such 9o devices are usually applied.

It is, of course, obvious that many sinds of split or sectional liolderinay be employed wiih the incloscd safety-strip, and that the the same maybe greatly varied without ai'ectV41 ing its functions.

It is desirable that the holder be ofinsulah ing material, and preferable that the inner faces, as in the present instance, be covered with a thin sheet of asbestus or like material, (shown `at c.)

yl. The combination of the scctionalholder; the sheathedor iucased safety-strip, and the I OO clamp. Constructed and arranged in substan- I strip, of an envelope 0F non-conducting intally the manner specified. combustible material consolidatef by press- 2. The combination. with the part I) of a I ure, as and. for the purpose ser, Form safety-strip holder having contact-plates se- In testimony whereof hzwfa hereunto set my cured thereto, of the part E133, with orrespondhand this 3d day of SeptembegQ 1884.

ing Contact-plates, a sheat ed oriucased safef Q fw ty-strip connect-ing the said contact-plates, WILLIAM I" JTM nds and clamping device for binding the parts 'Vitneses:

D and. E together, as herein seb forth. W. FRISBYs 3. The combiuatiqn, with a fusible safet),IY- PARKER W PAGE. 

